Nanosized particles of monoazo laked pigment with tunable properties

ABSTRACT

A nanoscale pigment particle composition includes an organic monoazo laked pigment including at least one functional moiety, and a sterically bulky stabilizer compound including at least one functional group, wherein the functional moiety on the pigment associates non-covalently with the functional group of the stabilizer; and the nanoscale pigment particles have an average particle size of from about 10 nm to about 500 nm and have tunable coloristic properties that depend on both particle composition and average particle size.

This application is a continuation-in-part of U.S. patent applicationSer. No. 11/759,913 to Rina Carlini et al. filed Jun. 7, 2007, theentire disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

This disclosure is generally directed to nanoscale pigment particlecompositions, and methods for producing such nanoscale pigment particlecompositions, as well as to uses of such compositions, for example, inink compositions. More specifically, this disclosure is directed toorganic mono-azo laked nanoscale pigments with tunable properties suchas particle size, coloristic properties, and properties as pigmentedliquid dispersions. Such particles are useful, for example, asnanoscopic colorants for such compositions as inks, toners and the like.

CROSS-REFERENCE TO RELATED APPLICATIONS

Disclosed in commonly assigned U.S. patent application Ser. No.11/759,913 to Rina Carlini et al. filed Jun. 7, 2007, is a nanoscalepigment particle composition, comprising: an organic monoazo lakedpigment including at least one functional moiety, and a sterically bulkystabilizer compound including at least one functional group, wherein thefunctional moiety associates non-covalently with the functional group;and the presence of the associated stabilizer limits the extent ofparticle growth and aggregation, to afford nanoscale-sized pigmentparticles. Also disclosed is a process for preparing nanoscale-sizedmonoazo laked pigment particles, comprising: preparing a first reactionmixture comprising: (a) a diazonium salt including at least onefunctional moiety as a first precursor to the laked pigment and (b) aliquid medium containing diazotizing agents generated in situ fromnitrous acid derivatives; and preparing a second reaction mixturecomprising: (a) a coupling agent including at least one functionalmoiety as a second precursor to the laked pigment and (b) a stericallybulky stabilizer compound having one or more functional groups thatassociate non-covalently with the coupling agent; and (c) a liquidmedium combining the first reaction mixture into the second reactionmixture to form a third mixture and effecting a direct coupling reactionwhich forms a monoazo laked pigment composition wherein the functionalmoiety associates non-covalently with the functional group and havingnanoscale particle size. Further disclosed is a process for preparingnanoscale monoazo laked pigment particles, comprising: providing amonoazo precursor dye to the monoazo laked pigment that includes atleast one functional moiety; subjecting the monoazo precursor dye to anion exchange reaction with a cation salt in the presence of a stericallybulky stabilizer compound having one or more functional groups; andprecipitating the monoazo laked pigment as nanoscale particles, whereinthe functional moiety of the pigment associates non-covalently with thefunctional group of the stabilizer and having nanoscale particle size.

Disclosed in commonly assigned U.S. patent application Ser. No.11/759,906 to Maria Birau et al. filed Jun. 7, 2007, is a nanoscalepigment particle composition, comprising: a quinacridone pigmentincluding at least one functional moiety, and a sterically bulkystabilizer compound including at least one functional group, wherein thefunctional moiety of the pigment associates non-covalently with thefunctional group of the stabilizer; and the presence of the associatedstabilizer limits the extent of particle growth and aggregation, toafford nanoscale-sized particles. Also disclosed is a process forpreparing nanoscale quinacridone pigment particles, comprising:preparing a first solution comprising: (a) a crude quinacridone pigmentor pigment precursor including at least one functional moiety and (b) aliquid medium; preparing a second solution comprising: (a) a stericallybulky stabilizer compound having one or more functional groups thatassociate non-covalently with the pigment functional moiety, and (b) aliquid medium; combining the first solution into the second solution toform a third reaction mixture which forms a quinacridone pigmentcomposition of nanoscale particle size and wherein the functional moietyof the pigment associates non-covalently with the functional group ofthe stabilizer. Still further is disclosed a process for preparingnanoscale quinacridone pigment particles, comprising: preparing a firstsolution comprising a quinacridone pigment including at least onefunctional moiety in an acid; preparing a second solution comprising anliquid medium and a sterically bulky stabilizer compound having one ormore functional groups that associate non-covalently with the functionalmoiety of the pigment; treating the second solution with the firstsolution to precipitate quinacridone pigment of nanoscale particle size,wherein the functional moiety of the pigment associates non-covalentlywith the functional group of the stabilizer.

The entire disclosure of the above-mentioned application is totallyincorporated herein by reference.

BACKGROUND

Pigments are a class of colorants useful in a variety of applicationssuch as, for example, paints, plastics and inks, including inkjetprinting inks. Dyes have typically been the colorants of choice forinkjet printing inks because they are readily soluble colorants whichenable jetting of the ink. Dyes have also offered superior and brilliantcolor quality with an expansive color gamut for inks, when compared withconventional pigments. However, since dyes are molecularly dissolved inthe ink vehicle, they are often susceptible to unwanted interactionsthat lead to poor ink performance, for example photooxidation from light(will lead to poor lightfastness), dye diffusion from the ink into paperor other substrates (will lead to poor image quality and showthrough),and the ability for the dye to leach into another solvent that makescontact with the image (will lead to poor water/solventfastness). Incertain situations, pigments are the better alternative as colorants forinkjet printing inks since they are insoluble and cannot be molecularlydissolved within the ink matrix, and therefore do not experiencecolorant diffusion. Pigments can also be significantly less expensivethan dyes, and so are attractive colorants for use in all printing inks.

Key challenges with using pigments for inkjet inks are their largeparticle sizes and wide particle size distribution, the combination ofwhich can pose critical problems with reliable jetting of the ink (i.e.inkjet nozzles are easily blocked). Pigments are rarely obtained in theform of single crystal particles, but rather as large aggregates ofcrystals and with wide distribution of aggregate sizes. The colorcharacteristics of the pigment aggregate can vary widely depending onthe aggregate size and crystal morphology. Thus, an ideal colorant thatis widely applicable in, for example, inks and toners, is one thatpossesses the best properties of both dyes and pigments, namely: 1)superior coloristic properties (large color gamut, brilliance, hues,vivid color); 2) color stability and durability (thermal, light,chemical and air-stable colorants); 3) minimal or no colorant migration;4) processable colorants (easy to disperse and stabilize in a matrix);and 5) inexpensive material cost. Thus, there is a need addressed byembodiments of the present invention, for small, nano-sized pigmentparticles that possess some or all of the aforementioned properties, inorder to minimize or avoid the problems associated with usingconventional larger-sized pigment particles in inks and toners. Thepresent nanosized pigment particles are useful in for example paints,coatings and inks (e.g., inkjet printing inks) and other compositionswhere pigments can be used such as plastics, optoelectronic imagingcomponents, photographic components and cosmetics among others.

Whether formulated for office printing or for production printing,printing inks and toners are expected to produce images that are robustand durable under stress conditions, such as exposure to abrasive orsharp objects or actions that produce a crease defect in the image (suchas folding or scratching the imaged paper). For example, in a typicaldesign of a piezoelectric ink jet device, the image is applied byjettingappropriately colored inks during four to six rotations (incrementalmovements) of a substrate (an image receiving member or intermediatetransfer member) with respect to the ink jetting head, i.e., there is asmall translation of the printhead with respect to the substrate inbetween each rotation. This approach simplifies the printhead design,and the small movements ensure good droplet registration. At the jetoperating temperature, droplets of liquid ink are ejected from theprinting device and, when the ink droplets contact the surface of therecording substrate, either directly or via an intermediate heatedtransfer belt or drum, they quickly solidify to form a predeterminedpattern of solidified ink drops. Inkjet printing inks comprised ofpigments should have appropriate viscosity characteristics under variousshear forces, so as to enable reliable jetting of the pigmented ink.There is a need to nano-sized pigments having suitable dispersion andviscosity properties to enable optimum jetting performance andultimately, printhead reliability.

The following documents provide background information:

Hideki Maeta et al., “New Synthetic Method of Organic Pigment NanoParticle by Micro Reactor System,” in an abstract available on theinternet, describes a new synthetic method of an organic pigment nanoparticle was realized by micro reactor. A flowing solution of an organicpigment, which dissolved in an alkaline aqueous organic solvent, mixedwith a precipitation medium in a micro channel. Two types of microreactor can be applied efficiently on this build-up procedure withoutblockage of the channel. The clear dispersion was extremely stable andhad narrow size distribution, which were the features, difficult torealize by the conventional pulverizing method (breakdown procedure).These results proved the effectiveness of this process on micro reactorsystem.

U.S. Patent Application Publication No. 2005/0109240 describes a methodof producing a fine particle of an organic pigment, containing the stepsof: flowing a solution of an organic pigment dissolved in an alkaline oracidic aqueous medium, through a channel which provides a laminar flow;and changing a pH of the solution in the course of the laminar flow.

WO 2006/132443 A1 describes a method of producing organic pigment fineparticles by allowing two or more solutions, at least one of which is anorganic pigment solution in which an organic pigment is dissolved, toflow through a microchannel, the organic pigment solution flows throughthe microchannel in a non-laminar state. Accordingly, the contact areaof solutions per unit time can be increased and the length of diffusionmixing can be shortened, and thus instantaneous mixing of solutionsbecomes possible. As a result, nanometer-scale monodisperse organicpigment fine particles can be produced in a stable manner.

U.S. Patent Application Publication No. 2003/0199608 discloses afunctional material comprising fine coloring particles having an averageprimary particle diameter of 1 to 50 nm in a dried state, and having aBET specific surface area value of 30 to 500 m.sup.2/g and a lighttransmittance of not less than 80%. The functional material composed offine coloring particles, exhibits not only an excellent transparency butalso a high tinting strength and a clear hue.

WO 2006/011467 discloses a pigment, which is used, for example, in colorimage display devices and can form a blue pixel capable of providing ahigh level of bright saturation, particularly a refined pigment, whichhas bright hue and is excellent in pigment properties such aslightfastness, solvent resistance and heat resistance, and a process forproducing the same, a pigment dispersion using the pigment, and an inkfor a color filter. The pigment is a subphthalocyanine pigment that isprepared by converting subphthalocyanine of the specified formula, to apigment, has diffraction peaks at least at diffraction angles (2θ) 7.0°,12.3°, 20.4° and 23.4° in X-ray diffraction and an average particlediameter of 120 to 20 nm.

U.S. Patent Application Publication No. 2006/0063873 discloses a processfor preparing nano water paint comprising the steps of: A. modifying thechemical property on the surface of nano particles by hydroxylation forforming hydroxyl groups at high density on the surface of the nanoparticles; B. forming self-assembly monolayers of low surface energycompounds on the nano particles by substituting the self-assemblymonolayers for the hydroxyl groups on the nano particles fordisintegrating the clusters of nano particles and for forming theself-assembly monolayers homogeneously on the surface of the nanoparticles; and C. blending or mixing the nano particles havingself-assembly monolayers formed thereon with organic paint to form nanowater paint.

WO 2006/005536 discloses a method for producing nanoparticles, inparticular, pigment particles. Said method consists of the followingsteps: (i) a raw substance is passed into the gas phase, (ii) particlesare produced by cooling or reacting the gaseous raw substance and (iii)an electrical charge is applied to the particles during the productionof the particles in step (ii), in a device for producing nanoparticles.The disclosure further relates to a device for producing nanoparticles,comprising a supply line, which is used to transport the gas flow intothe device, a particle producing and charging area in order to produceand charge nanoparticles at essentially the same time, and an evacuationline which is used to transport the charged nanoparticles from theparticle producing and charging area.

Japanese Patent Application Publication No. JP 2005238342 A2 disclosesirradiating ultrashort pulsed laser to organic bulk crystals dispersedin poor solvents to induce ablation by nonlinear absorption for crushingthe crystals and recovering the resulting dispersions of scatteredparticles. The particles with average size approximately 10 nm areobtained without dispersants or grinding agents for contaminationprevention and are suitable for pigments, pharmaceuticals, etc.

U.S. Pat. No. 6,837,918 discloses a process and apparatus that collectspigment nanoparticles by forming a vapor of a pigment that is solid atroom temperature, the vapor of the pigment being provided in an inertgaseous carrying medium. At least some of the pigment is solidifiedwithin the gaseous stream. The gaseous stream and pigment material ismoved in a gaseous carrying environment into or through a dry mechanicalpumping system. While the particles are within the dry mechanicalpumping system or after the nanoparticles have moved through the drypumping system, the pigment material and nanoparticles are contactedwith an inert liquid collecting medium.

U.S. Pat. No. 6,537,364 discloses a process for the fine division ofpigments which comprises dissolving coarsely crystalline crude pigmentsin a solvent and precipitating them with a liquid precipitation mediumby spraying the pigment solution and the precipitation medium throughnozzles to a point of conjoint collision in a reactor chamber enclosedby a housing in a microjet reactor, a gas or an evaporating liquid beingpassed into the reactor chamber through an opening in the housing forthe purpose of maintaining a gas atmosphere in the reactor chamber, andthe resulting pigment suspension and the gas or the evaporated liquidbeing removed from the reactor through a further opening in the housingby means of overpressure on the gas entry side or underpressure on theproduct and gas exit side.

U.S. Pat. No. 5,679,138 discloses a process for making ink jet inks,comprising the steps of: (A) providing an organic pigment dispersioncontaining a pigment, a carrier for the pigment and a dispersant; (B)mixing the pigment dispersion with rigid milling media having an averageparticle size less than 100 μm; (C) introducing the mixture of step (B)into a high speed mill; (D) milling the mixture from step (C) until apigment particle size distribution is obtained wherein 90% by weight ofthe pigment particles have a size less than 100 nanometers (nm); (E)separating the milling media from the mixture milled in step (D); and(F) diluting the mixture from step (E) to obtain an ink jet ink having apigment concentration suitable for ink jet printers.

Japanese Patent Application Publications Nos. JP 2007023168 and JP2007023169 discloses providing a pigment dispersion compound excellentin dispersibility and flowability used for the color filter which hashigh contrast and weatherability. The solution of the organic material,for example, the organic pigment, dissolved in a good solvent under theexistence of alkali soluble binder (A) which has an acidic group, and apoor solvent which makes the phase change to the solvent are mixed. Thepigment nanoparticles dispersed compound re-decentralized in the organicsolvent containing the alkali soluble binder (B) which concentrates theorganic pigment nanoparticles which formed the organic pigment as theparticles of particle size less than 1 μm, and further has the acidicgroup.

Kazuyuki Hayashi et al., “Uniformed nano-downsizing of organic pigmentsthrough core-shell structuring,” Journal of Materials Chemistry, 17(6),527-530 (2007) discloses that mechanical dry milling of organic pigmentsin the presence of mono-dispersed silica nanoparticles gave core-shellhybrid pigments with uniform size and shape reflecting those of theinorganic particles, in striking contrast to conventional milling as abreakdown process, which results in limited size reduction and wide sizedistribution.

U.S. Patent Application Publication No. 2007/0012221 describes a methodof producing an organic pigment dispersion liquid, which has the stepsof: providing an alkaline or acidic solution with an organic pigmentdissolved therein and an aqueous medium, wherein a polymerizablecompound is contained in at least one of the organic pigment solutionand the aqueous medium; mixing the organic pigment solution and theaqueous medium; and thereby forming the pigment as fine particles; thenpolymerizing the polymerizable compound to form a polymer immobile fromthe pigment fine particles.

K. Balakrishnan et al., “Effect of Side-Chain Substituents onSelf-Assembly of Perylene Diimide Molecules: Morphology Control,” J. Am.Chem. Soc., vol. 128, p. 7390-98 (2006) describes the use ofcovalently-linked aliphatic side-chain substituents that werefunctionalized onto perylene diimide molecules so as to modulate theself-assembly of molecules and generate distinct nanoparticlemorphologies (nano-belts to nano-spheres), which in turn impacted theelectronic properties of the material. The side-chain substituentsstudied were linear dodecyl chain, and a long branched nonyldecyl chain,the latter substituent leading to the more compact, sphericalnanoparticle.

The appropriate components and process aspects of each of the foregoingmay be selected for the present disclosure in embodiments thereof, andthe entire disclosure of the above-mentioned references are totallyincorporated herein by reference.

SUMMARY

The present disclosure addresses these and other needs, by providingnanoscale pigment particle compositions, and methods for producing suchnanoscale pigment particle compositions.

In an embodiment, the present disclosure provides a nanoscale pigmentparticle composition, comprising:

an organic monoazo laked pigment including at least one functionalmoiety, and

a sterically bulky stabilizer compound including at least one functionalgroup,

wherein the functional moiety of the pigment associates non-covalentlywith the functional group of the stabilizer; and

the nanoscale pigment particles have an average particle size rangingfrom about 10 nm to about 500 nm and have tunable coloristic properties.For example, when dispersed in a colorless, transparent polymer binderfor making thin film coatings, the nanoscale particles of monoazo lakedpigments exhibit coloristic properties that are correlated and tunablewith average pigment particle size as well as the composition of thepigment with associated stabilizer.

In another embodiment, the present disclosure provides processes forpreparing nanoscale-sized monoazo laked pigment particles, comprising:

providing an organic pigment precursor to a monoazo laked pigment thatcontains at least one functional moiety,

providing a sterically bulky stabilizer compound that contains at leastone functional group, and

carrying out a chemical reaction to form a monoazo laked pigmentcomposition, whereby the functional moiety found on the pigmentprecursor is incorporated within the monoazo laked pigment andnon-covalently associated with the functional group of the stabilizer,so as to allow the formation of nanoscale-sized pigment particles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a b* a* Gamut for pigmented coatings prepared with examplePR57:1 pigments (Magenta Optical Density=1.5).

FIG. 2 shows a relationship between hue angle and normalized lightscatter index (NLSI) for pigmented coatings on Mylar film, preparedaccording to embodiments (Magenta Optical Density=1.5).

FIG. 3 shows a relationship between hue angle of pigmented coatings andZ-average particle size prepared with example PR57:1 pigments (MagentaOptical Density=1.5).

FIG. 4 shows a relationship between normalized light scatter index ofpigmented coatings and Z-average particle size prepared with examplePR57:1 pigments (Magenta Optical Density=1.5).

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Embodiments of the present disclosure provide nanoscale pigment particlecompositions, and methods for producing such nanoscale pigment particlecompositions. The nanoscale pigment particle compositions generallycomprise an organic monoazo laked pigment including at least onefunctional moiety that associates non-covalently with a functional groupfrom a sterically bulky stabilizer compound. The presence of theassociated stabilizer limits the extent of particle growth andaggregation, to afford nanoscale particles. The nanoscale pigmentparticles have an average particle size of from about 10 nm to about 500nm and have coloristic properties that are that are correlated andtunable with average pigment particle size as well as the composition ofthe pigment and associated stabilizer.

Organic monoazo “laked” pigments are the insoluble metal salt colorantsof monoazo colorants which can include monoazo dyes or pigments, and incertain geographic regions these pigments have been referred to aseither “toners” or “lakes”. The process of ion complexation with a metalsalt, or “laking” process, provides decreased solubility of thenon-ionic monoazo pigment, which can enhance the migration resistanceand thermal stability properties of a monoazo pigment, and therebyenable the applications of such pigments for robust performance, such ascolorizing plastics and heat-stable paints for outdoor use. Formula 1depicts a general representation of monoazo laked pigments, which areionic compounds that are structurally comprised of a diazo group(denoted G_(d)) and a nucleophilic coupling group (denoted as G_(c))that are linked together with one azo (N═N) functional group, and acation (M^(n+)) which is typically a metal salt. Either or both of thegroups G_(d) and G_(c) can contain one or more ionic functional moieties(denoted as FM), such as sulfonate or carboxylate anions or the like.

As an example, the organic monoazo laked pigment PR 57:1 (“PR” refers toPigment Red) has two functional moieties of two different types, asulfonate anion group (SO₃ ⁻) and carboxylate anion group (CO₂ ⁻) and ametal counter-cation M^(n+) that is chosen from Group 2 alkaline earthmetals such as Ca²⁺. Other monoazo laked pigment compositions also existthat have a counter-cattion chosen from either Group 2 alkaline earthmetals (Be, Mg, Ca, Sr, Ba,), Group 3 metals (B, Al, Ga), Group 1 alkalimetals (Li, Na, K, Cs), the transition metals such as Cr, Mn, Fe, Ni,Cu, Zn, or others non-metallic cations such as ammonium (NR₄ ⁺),phosphonium (PR₄ ⁺) wherein R-group can be H or alkyl group having fromabout 1 to about 12 carbons. Further, the azo group in the compounds cangenerally assume one or more tautomeric forms, such as the “azo”tautomer form which has the (N═N) linkage, and the “hydrazone” tautomerform which has the (C═N—NH—) linkage that is stabilized by anintramolecular hydrogen bond, where the hydrazone tautomer is known tobe the preferred structural form for PR 57:1.

It is understood that formula (1) is understood to denote both suchtautomer forms. Due to the structural nature of monoazo laked pigmentsbeing ionic salts, it is possible to have compounds that associatenon-covalently with the pigment, such as organic or inorganic ioniccompounds that can associate with the metal cation through ionic orcoordination-type bonding. Such ionic compounds are included in a groupof compounds which herein are referred to as “stabilizers”, and thatfunction to reduce the surface tension of the pigment particle andneutralize attractive forces between two or more pigment particles orstructures, thereby stabilizing the chemical and physical structure ofthe pigment. The term “complementary” as used in “complementaryfunctional moiety” of the stabilizer indicates that the complementaryfunctional moiety is capable of noncovalent chemical bonding with thefunctional moiety of the organic pigment and/or the functional moiety ofa pigment precursor.

The term “precursor” as used in “precursor to the organic pigment” canbe any chemical substance that is an advanced intermediate in the totalsynthesis of a compound (such as the organic pigment). In embodiments,the organic pigment and the precursor to the organic pigment may or maynot have the same functional moiety. In embodiments, the precursor tothe organic pigment may or may not be a colored compound. In still otherembodiments, the precursor and the organic pigment can have differentfunctional moieties. In embodiments, where the organic pigment and theprecursor have a structural feature or characteristic in common, thephrase “organic pigment/pigment precursor” is used for conveniencerather than repeating the same discussion for each of the organicpigment and the pigment precursor.

The functional moiety (denoted as FM) of the organic pigment/precursorcan be any suitable moiety capable of non-covalent bonding with thecomplementary functional group of the stabilizer. Illustrativefunctional moieties of the organic pigment/precursor include (but arenot limited to) the following: sulfonate/sulfonic acid,(thio)carboxylate/(thio)carboxylic acid, phosphonate/phosphonic acid,ammonium and substituted ammonium salts, phosphonium and substitutedphosphonium salts, substituted carbonium salts, substituted aryliumsalts, alkyl/aryl (thio)carboxylate esters, thiol esters, primary orsecondary amides, primary or secondary amines, hydroxyl, ketone,aldehyde, oxime, hydroxylamino, enamines (or Schiff base), porphyrins,(phthalo)cyanines, urethane or carbamate, substituted ureas, guanidinesand guanidinium salts, pyridine and pyridinium salts, imidazolium and(benz)imidazolium salts, (benz)imidazolones, pyrrolo, pyrimidine andpyrimidinium salts, pyridinone, piperidine and piperidinium salts,piperazine and piperazinium salts, triazolo, tetraazolo, oxazole,oxazolines and oxazolinium salts, indoles, indenones, and the like.

Pigment precursors for making monoazo laked nanopigments consist of asubstituted aniline precursor (denoted as “DC” in Table 1) which formsthe diazo group G_(d) of Formula (1), a nucleophilic or basic couplingcompound (denoted as “CC” in Tables 2-6) which leads to the couplinggroup G_(c) of Formula (1), and a cation salt which is preferably ametal (denoted as “M” as shown in Formula (1)). Representative examplesof the aniline precursor of laked monoazo pigments that have thefunctional moiety capable of non-covalent bonding with a complementaryfunctional group on the stabilizer, include (but are not limited to) thefollowing structures (with the functional moiety “FM” denoted, ifapplicable).

In an embodiment, the substituted aniline precursor (DC) which leads tothe diazonium group can be of the formula (2):

where R₁, R₂, and R₃ independently represent H, a straight or branchedalkyl group of from about 1 to about 10 carbon atoms (such as methyl,ethyl, propyl, butyl, and the like), halogen (such as Cl, Br, I), NH₂,NO₂, CO₂H, CH₂CH₃, and the like; and functional moiety FM representsSO₃H, —C(═O)—NH-Aryl-SO₃ ⁻ where the aryl group can be unsubstituted orsubstituted with either halogens (such as Cl, Br, I, F) or alkyl groupshaving from about 1 to about 10 carbons (such as methyl, ethyl, propyl,butyl and the like) CO₂H, halogen (such as Cl, Br, I), NH₂, —C(═O)—NH₂,and the like. The substituted aniline precursor (DC) can be also beTobias Acid, of the formula (3):

Specific examples of types of aniline precursors (DC) that are used tomake the diazo group G_(d) in the monoazo laked pigments include thoseof Table 1:

TABLE 1

Functional Precursor to Moiety Group G_(d) FM R₁ R₂ R₃ DC1 SO₃H CH₃ HNH₂ DC2 SO₃H CH₃ Cl NH₂ DC3 SO₃H Cl CH₃ NH₂ DC4 SO₃H Cl CO₂H NH₂ DC5SO₃H Cl CH₂CH₃ NH₂ DC6 SO₃H Cl Cl NH₂ DC7 SO₃H H NH₂ H DC8 SO₃H H NH₂CH₃ DC9 SO₃H NH₂ H Cl DC10 SO₃H H H NH₂ DC11 SO₃H H NH₂ H DC12 SO₃H NO₂NH₂ H DC13

NH₂ CH₃ H DC14 CO₂H H H NH₂ DC15 Cl H H NH₂ DC16 NH₂ CH₃ H H DC17 NH₂ HCH₃ H DC18

NH₂ CH₃ H DC19

H NH₂ H DC20 NH₂ H H H DC21

In an embodiment, the coupling group G_(c) of Formula (1) can includeβ-naphthol and derivatives of Formula (4), naphthalene sulfonic acidderivatives of Formulas (5) and (6), pyrazolone derivatives of Formula(7), acetoacetic arylide derivatives of Formula (8), and the like. Informulas (4)-(8), the asterisk “*” denotes the point of coupling orattachment to the monoazo (N═N) linkage.

where FM represents H, CO₂H, SO₃H, —C(═O)—NH-Aryl-SO₃ ⁻ where the arylgroup can be unsubstituted or substituted with either halogens (such asCl, Br, I, F) or alkyl groups having from about 1 to about 10 carbons(such as methyl, ethyl, propyl, butyl and the like) CO₂H, halogen (suchas Cl, Br, I), NH₂, —C(═O)—NH₂, substituted benzamides such as:

wherein groups R₂′ R₃′, R₄′ and R₅′ can independently be H, alkyl groupshaving from about 1 to 10 carbons (such as methyl, ethyl, propyl, butyl,and the like), alkoxyl groups (such as OCH₃, OCH₂CH₃, and the like),hydroxyl or halogen (such as Cl, Br, I, F) or nitro NO₂; orbenzimidazolone amides such as:

and the like.

where FM represents preferably SO₃H, but also can represent CO₂H,—C(═O)—NH-Aryl-SO₃ ⁻ where the aryl group can be unsubstituted orsubstituted with either halogens (such as Cl, Br, I, F) or alkyl groupshaving from about 1 to about 10 carbons (such as methyl, ethyl, propyl,butyl and the like) CO₂H, halogen (such as Cl, Br, I), NH₂, —C(═O)—NH₂groups R₃ and R₄ independently represent H, SO₃H, and the like.

where FM represents preferably SO₃H, but also can represent CO₂H,—C(═O)—NH-Aryl-SO₃ ⁻ where the aryl group can be unsubstituted orsubstituted with either halogens (such as Cl, Br, I, F) or alkyl groupshaving from about 1 to about 10 carbons (such as methyl, ethyl, propyl,butyl and the like) CO₂H, halogen (such as Cl, Br, I), NH₂, —C(═O)—NH₂;R₁, R₂, R₃ and R₄ independently represent H, SO₃H, —C(═O)—NH-Phenyl, andthe like.

where G represents CO₂H, straight or branched alkyl such as having from1 to about 10 carbons atoms (such as methyl, ethyl, propyl, butyl, orthe like), and the like; and R₁′, R₂′, R₃′ and R₄′ independentlyrepresent H, halogen (such as Cl, Br, I), SO₃H, nitro (NO₂) or alkoxylgroup such as OCH₃ or OCH₂CH₃ and the like.

where R₁′ represents a straight or branched alkyl group having, forexample, from 1 to about 10 carbon atoms (such as methyl, ethyl, propyl,butyl, and the like); R₂′ represents a benzimidazolone group:

or a substituted aryl group

where each of R_(a), R_(b), and R_(c) independently represents H, astraight or branched alkyl group having, for example, from 1 to about 10carbon atoms (such as methyl, ethyl, propyl, butyl, and the like),alkoxyl groups such as OCH₃ or OCH₂CH₃ and the like, halogen (such asCl, Br, I), nitro NO₂, and the like.

Representative examples of the nucleophilic coupling component as aprecursor of laked monoazo pigments which have the functional moietythat is capable of non-covalent bonding with a complementary functionalgroup on the stabilizer, include (but are not limited to) the followingstructures shown in Tables 2-6 (with the functional moiety “FM” denoted,if applicable):

TABLE 2

Precursor to Class of Coupling Functional Moiety group G_(c) ComponentFM CC1 β-Naphthol H CC2 β-oxynaphthoic CO₂H acid (“BONA”) CC3 NaphtholASderivatives

CC6 Benzimidazolone

TABLE 3

Precursor to Class of Coupling group G_(c) Component FM R₃ R₄ CC4aNaphthalene Sulfonic SO₃H H H Acid derivatives CC4b Naphthalene SulfonicSO₃H SO₃H H Acid derivatives

TABLE 4

* = point of coupling to diazo component Precursor Class of to Couplinggroup G_(c) Component FM R₁ R₂ R₃ R₄ CC5NaphthaleneSulfonicAcidderivatives SO₃H

H H SO₃H

TABLE 5

Precursor to Class of Coupling group G_(c) Component G R₁′ R₂′ R₃′ R₄′CC7 Pyrazolone deriv. CO₂H H H SO₃H H CC8 Pyrazolone deriv. CH₃ H H SO₃HH CC9 Pyrazolone deriv. CH₃ H SO₃H H H  CC10 Pyrazolone deriv. CH₃ Cl HSO₃H Cl

TABLE 6

Precursor to Class of Coupling group G_(c) Component R₁′ R₂′ R_(a) R_(b)R_(c) CC11 Acetoacetic arylide CH₃

H H H CC12 Acetoacetic arylide CH₃

CH₃ H H CC13 Acetoacetic arylide CH₃

Cl H H CC14 Acetoacetic arylide CH₃

H OCH₃ H CC15 Acetoaceticbenzimidazolone CH₃

— — —

The organic pigment, and in some embodiments, the organic pigmentprecursor, also generally includes a counterion as part of the overallstructure. Such counterions can be, for example, any suitable counterionincluding those that are well known in the art. Such counterions can be,for example, cations or anions of either metals or non-metals thatinclude N, P, S and the like, or carbon-based cations or anions.Examples of suitable cations include ions of Ba, Ca, Cu, Mg, Sr, Li, Na,K, Cs, Mn, Cu, Cr, Fe, Ti, Ni, Co, Zn, V, B, Al, Ga, and other metalions, as well as ammonium and phosphonium cations, mono-, di-, tri-, andtetra-substituted ammonium and phosphonium cations, where thesubstitutents can be aliphatic alkyl groups, such as methyl, ethyl,butyl, stearyl and the like, as well as aryl groups such as phenyl orbenzyl and the like.

Representative examples of monoazo laked pigments comprised from aselection of substituted aniline precursors (denoted DC) which can alsoinclude Tobias Acid, nucleophilic coupling component (denoted as CC) andmetal salts (denoted as M) to provide the counter-cation M^(n+) offormula (1) are listed in Table 7, and other laked pigment structuresmay arise from other combinations of DC and CC and metal cation salt (M)that are not shown in Table 7.

TABLE 7

Color Index # Color Index G_(d) G_(c) Metal Salt (C.I.) (C.I.) NameLaked Pigment Class precursor precursor M 15500:1 Red 50:1 β-NaphtholLakes  DC14 CC1 ½ Ba 15510:1 Orange 17 β-Naphthol Lakes DC7 CC1 Ba15510:2 Orange 17:1 β-Naphthol Lakes DC7 CC1 ⅔ Al 15525   Red 68β-Naphthol Lakes DC4 CC1 2 Ca 15580   Red 51 β-Naphthol Lakes DC8 CC1 Ba15585   Red 53 β-Naphthol Lakes DC3 CC1 2 Na 15585:1 Red 53:1 β-NaphtholLakes DC3 CC1 Ba 15585:3 Red 53:3 β-Naphthol Lakes DC3 CC1 Sr 15602  Orange 46 β-Naphthol Lakes DC5 CC1 Ba 15630   Red 49 β-Naphthol Lakes DC21 CC1 2 Na 15630:1 Red 49:1 β-Naphthol Lakes  DC21 CC1 Ba 15630:2Red 49:2 β-Naphthol Lakes  DC21 CC1 Ca 15630:3 Red 49:3 β-Naphthol Lakes DC21 CC1 Sr 15800   Red 64 β-oxynaphthoic acid (BONA) Lakes  DC20 CC2½ Ba 15800:1 Red 64:1 β-oxynaphthoic acid (BONA) Lakes  DC20 CC2 ½ Ca15800:2 Brown 5 β-oxynaphthoic acid (BONA) Lakes  DC20 CC2 ½ Cu 15825:2Red 58:2 β-oxynaphthoic acid (BONA) Lakes DC9 CC2 Ca 15825:4 Red 58:4β-oxynaphthoic acid (BONA) Lakes DC9 CC2 Mn 15850:1 Red 57:1β-oxynaphthoic acid (BONA) Lakes DC1 CC2 Ca 15860:1 Red 52:1β-oxynaphthoic acid (BONA) Lakes DC3 CC2 Ca 15860:2 Red 52:2β-oxynaphthoic acid (BONA) Lakes DC3 CC2 Mn 15865:1 Red 48:1β-oxynaphthoic acid (BONA) Lakes DC2 CC2 Ba 15865:2 Red 48:2β-oxynaphthoic acid (BONA) Lakes DC2 CC2 Ca 15865:3 Red 48:3β-oxynaphthoic acid (BONA) Lakes DC2 CC2 Sr 15865:4 Red 48:4β-oxynaphthoic acid (BONA) Lakes DC2 CC2 Mn 15865:5 Red 48:5β-oxynaphthoic acid (BONA) Lakes DC2 CC2 Mg 15867   Red 200β-oxynaphthoic acid (BONA) Lakes DC5 CC2 Ca 15880:1 Red 63:1β-oxynaphthoic acid (BONA) Lakes  DC21 CC2 Ca 15880:2 Red 63:2β-oxynaphthoic acid (BONA) Lakes  DC21 CC2 Mn 15892   Red 151 NaphtholAS Lakes  DC10 CC3 Ba (R₂′ = H, R₄′ = SO₃H) 15910   Red 243 Naphthol ASLakes DC2 CC3 ½ Ba (R₂′ = OCH₃, R₄′ = H) 15915   Red 247 Naphthol ASLakes  DC13 CC3 Ca (R₂′ = H, R₄′ = OCH₃) 15985:1 Yellow 104 NaphthaleneSulfonic Acid Lakes DC7 CC4a ⅔ Al 15990   Orange 19 Naphthalene SulfonicAcid Lakes  DC15 CC4a ½ Ba 16105   Red 60 Naphthalene Sulfonic AcidLakes  DC14 CC4b 3/2 Ba 18000:1 Red 66 Naphthalene Sulfonic Acid Lakes DC16 CC5 ½ Ba, Na

The complementary functional group of the stabilizer can be one or moreof any suitable moiety capable of non-covalent bonding with thefunctional moiety of the stabilizer. Illustrative complementaryfunctional groups on the stabilizer include the following:sulfonate/sulfonic acid, (thio)carboxylate/(thio)carboxylic acid,phosphonate/phosphonic acid, ammonium and substituted ammonium salts,phosphonium and substituted phosphonium salts, substituted carboniumsalts, substituted arylium salts, alkyl/aryl (thio)carboxylate esters,thiol esters, primary or secondary amides, primary or secondary amines,hydroxyl, ketone, aldehyde, oxime, hydroxylamino, enamines (or Schiffbase), porphyrins, (phthalo)cyanines, urethane or carbamate, substitutedureas, guanidines and guanidinium salts, pyridine and pyridinium salts,imidazolium and (benz)imidazolium salts, (benz)imidazolones, pyrrolo,pyrimidine and pyrimidinium salts, pyridinone, piperidine andpiperidinium salts, piperazine and piperazinium salts, triazolo,tetraazolo, oxazole, oxazolines and oxazolinium salts, indoles,indenones, and the like.

The stabilizer can be any compound that has the function of limiting theextent of pigment particle or molecular self-assembly so as to producepredominantly nanoscale-sized pigment particles. The stabilizer compoundshould have a hydrocarbon moiety that provides sufficient steric bulk toenable the function of the stabilizer to regulate pigment particle size.The hydrocarbon moiety in embodiments is predominantly aliphatic, but inother embodiments can also incorporate aromatic groups, and generallycontains at least 6 carbon atoms, such as at least 12 carbons or atleast 16 carbons, and not more than about 100 carbons, but the actualnumber of carbons can be outside of these ranges. The hydrocarbon moietycan be either linear, cyclic or branched, and in embodiments isdesirably branched, and may or may not contain cyclic moieties such ascycloalkyl rings or aromatic rings. The aliphatic branches are long withat least 2 carbons in each branch, such as at least 6 carbons in eachbranch, and not more than about 100 carbons.

It is understood that the term “steric bulk” is a relative term, basedon comparison with the size of the pigment or pigment precursor to whichit becomes non-covalently associated. In embodiments, the phrase “stericbulk” refers to the situation when the hydrocarbon moiety of thestabilizer compound that is coordinated to the pigment/precursorsurface, occupies a 3-dimensional spatial volume that effectivelyprevents the approach or association of other chemical entities (e.g.colorant molecules, primary pigment particles or small pigmentaggregate) toward the pigment/precursor surface. Thus, the stabilizershould have its hydrocarbon moiety large enough so that as severalstabilizer molecules become non-covalently associated with the chemicalentity pigment or precursor), the stabilizer molecules act as surfacebarrier agents for the primary pigment particles and effectivelyencapsulates them, and thereby limits the growth of the pigmentparticles and affording only nanoparticles of the pigment. For example,for the pigment precursor Lithol Rubine and for the organic pigmentPigment Red 57:1, the following illustrative groups on a stabilizer areconsidered to have adequate “steric bulk” so as to enable the stabilizerto limit the extent of pigment self-assembly or aggregation and mainlyproduce pigment nano-sized particles:

Representative examples of stabilizer compounds that have both thefunctional group that non-covalently associates with the pigment and thesterically bulky hydrocarbon moiety, include (but are not limited to)the following compounds:

wherein m and n denotes the number of repeated methylene units, andwhere m can range between 1 and 50, and n can range between 1 and 5,however the values can also be outside these ranges.

In additional embodiments, other stabilizer compounds having differentstructures than those described previously may be used in addition tosterically bulky stabilizer compounds, to function as surface activeagents (or surfactants) that either prevent or limit the degree ofpigment particle aggregation. Representative examples of such surfaceactive agents include, but are not limited to, rosin natural productssuch as abietic acid, dehydroabietic acid, pimaric acid, rosin soaps(such as the sodium salt of the rosin acids), hydrogenated derivativesof rosins and their alkyl ester derivatives made from glycerol orpentaerythritol or other such hydrocarbon alcohols, acrylic-basedpolymers such as poly(acrylic acid), poly(methyl methacrylate),styrene-based copolymers such as poly(styrene sodio-sulfonate) andpoly(styrene)-co-poly(alkyl (meth)acrylate), copolymers of α-olefinssuch as 1-hexadecene, 1-octadecene, 1-eicosene, 1-triacontene and thelike, copolymers of 4-vinyl pyridine, vinyl imidazole, and vinylpyrrolidinone, polyester copolymers, polyamide copolymers, copolymers ofacetals and acetates, such as the copolymer poly(vinylbutyral)-co-(vinylalcohol)-co-(vinyl acetate).

The types of non-covalent chemical bonding that can occur between thefunctional moiety of the precursor/pigment and the complementaryfunctional group of the stabilizer are, for example, van der Waals'forces, ionic or coordination bonding, hydrogen bonding, and/or aromaticpi-stacking bonding. In embodiments, the non-covalent bonding ispredominately ionic bonding, but can include hydrogen bonding andaromatic pi-stacking bonding as additional or alternative types ofnon-covalent bonding between the functional moieties of the stabilizercompounds and the precursor/pigment.

The “average” pigment particle size, which is typically represented byZ-average, which is defined as an intensity mean which is derived fromthe cumulants analysis of an intensity signal obtained from dynamiclight scattering method, and also by d₅₀, which is defined as the medianparticle size value at the 50th percentile of the particle sizedistribution, wherein 50% of the particles in the distribution aregreater than the d₅₀ particle size value and the other 50% of theparticles in the distribution are less than the d₅₀ value. Averageparticle size can be measured by methods that use light scatteringtechnology to infer particle size, such as by dynamic light scattering(DLS). The term “particle diameter” as used herein refers to the lengthof the pigment particle at the longest dimension (in the case ofacicular shaped particles) as derived from images of the particlesgenerated by Transmission Electron Microscopy (TEM). The term“nano-sized”, “nanoscale”, “nanoscopic”, or “nano-sized pigmentparticles” refers to for instance, an average particle size, d₅₀, orZ-average, or an average particle diameter of less than about 150 nm,such as of about 1 nm to about 100 nm, or about 10 nm to about 80 nm.Typically, the distribution of a population of particle sizes isexpressed by a width parameter or the polydispersity index (PDI), suchas can be derived by DLS technique, and also by geometric standarddeviation (GSD) which is a dimensionless number that typically estimatesa population's dispersion of a given attribute (for instance, particlesize) about the median value of the population and is derived from theexponentiated value of the standard deviation of the log-transformedvalues. If the geometric mean (or median) of a set of numbers {A₁, A₂, .. . , A_(n)} is denoted as μ_(g), then the geometric standard deviationis calculated as:

$\sigma_{g} = {\exp\sqrt{\frac{\sum\limits_{i = 1}^{n}\;\left( {{\ln\mspace{14mu} A_{i}} - {\ln\mspace{14mu}\mu_{g}}} \right)^{2}}{n}}}$

The method of making nano-sized particles of the monoazo laked pigmentssuch as those listed in Table 7 is a process that involves at least oneor more reaction steps. A diazotization reaction is a key reaction stepfor synthesis of the monoazo laked pigment, whereby a suitablysubstituted aniline precursor (denoted as diazo component DC) such asthose listed in Table 1, and Formulas (2) and (3), is either directly orindirectly converted first to a diazonium salt using standardprocedures, such as that which includes treatment with an effectivediazotizing agent such as nitrous acid HNO₂ (which is generated in situby mixing sodium nitrite with dilute protic acid solution such ashydrochloric acid), or nitrosyl sulfuric acid (NSA), which iscommercially available or can be prepared by mixing sodium nitrite inconcentrated sulfuric acid. Initially, it may be necessary to firstdissolve the precursor substituted aniline in alkaline solution (such asaqueous potassium hydroxide solution, or ammonia water) followed bytreatment with the diazotizing agent and acid solution, so as togenerate the diazonium salt. The diazotization procedure is typicallycarried out at cold temperatures so as to keep the diazonium saltstable, and the resulting reaction mixture will comprise mainly thediazonium salt either dissolved or suspended as a precipitate in acidicmedium. If desired and effective, an aqueous solution of the metal salt(M^(n+)) can be optionally added that will define the specificcomposition of the desired monoazo laked pigment product, such as thoselisted in Table 7. A second solution or suspension is prepared bydissolving or suspending the nucleophilic coupling component (denoted asCC, such as those shown in Tables 2-6, and Formulas (4)-(8)) mainly intowater, which may optionally contain another liquid such as an organicsolvent (for example, iso-propanol, tetrahydrofuran, methanol, orother), and either acids or bases to render the coupling component intosolution or a fine suspension and aid reaction with the diazonium saltsolution, and additionally any buffers or surface active agentsincluding the sterically bulky stabilizer compounds such as thosedescribed previously.

The reaction mixture containing the dissolved or suspended diazoniumsalt is then transferred into the solution or suspension of the desirednucleophilic coupling component, and the temperature of the mixture canrange from about 10° C. to about 75° C., in order to produce a solidcolorant material suspended as a precipitate in an aqueous slurry.

The solid colorant material may be the desired monoazo laked pigmentproduct formed as nano-sized particles, or it may be an advancedsynthetic intermediate for making the monoazo laked pigment product. Inthe case of the latter, a two-step process is required for preparing thenano-sized particles of monoazo laked pigment, whereby the second stepinvolves rendering the advanced synthetic intermediate of the first stepabove (the pigment precursor) into homogeneous liquid solution bytreatment with either strong acid or alkaline base, then treating thissolution with one or more surface active agents in addition to thesterically bulky stabilizer compounds, as described previously, followedlastly by treatment with the required metal salt solution to provide thedesired laked monoazopigment composition as a solid precipitate, saidmetal salt solution effectively functioning as a pigment precipitatingagent. There are several chemical as well as physical processing factorscan affect the final particle size and distribution of the monoazo lakedpigment nanoparticles, including stoichiometries of the DC and CCstarting reactants, metal salt, surface active agents, and stabilizercompounds, the concentrations of chemical species in the liquid medium,pH of liquid medium, temperature, addition rate, order of addition,agitation rate, post-reaction treatments such as heating, isolation andwashing of particles, and drying conditions.

In embodiments is disclosed a two-step method of making nano-sizedmonoazo laked red pigments, for example Pigment Red 57:1, wherein theadvanced pigment precursor Lithol Rubine is first synthesized as apotassium salt and is a water-soluble orange dye. The first stepinvolves the diazotization of 2-amino-5-methyl-benzenesulfonic acid (DC1in Table 1) by first dissolving the DC in dilute aqueous potassiumhydroxide solution (0.5 mol/L) and cooling to a temperature anywhere inthe range of about −5° C. to about 5° C., and then treating the solutionwith an aqueous solution of sodium nitrite (20 wt %), following withslow addition of concentrated hydrochloric acid at a rate that maintainsthe internal reaction temperature between −5° C. and +5° C. Theresulting suspension that forms is stirred for additional time so as toensure completeness of diazotization, and then the suspension iscarefully transferred to a second solution containing3-hydroxy-2-naphthoic acid dissolved in dilute alkaline solution (0.5mol/L potassium hydroxide), using vigorous agitation as the colorantproduct is produced in the aqueous slurry. After stirring for additionaltime of at least 1 hour at room temperature, the colorant product(Lithol Rubine-potassium salt) is isolated by filtration as an orangedyestuff and washed with deionized water to remove excess saltby-products.

The second step of the process involves redispersing the orange LitholRubine-potassium salt dyestuff in deionized water to a concentrationthat can range from about 0.5 wt % to about 20 wt %, such as from about1.5 wt % to about 10 wt % or from about 3.5 wt % to about 8 wt %, butthe concentrations can also be outside of these ranges. The colorantsolids in the slurry is then dissolved completely into liquid solutionby treatment with aqueous alkaline base, such as sodium hydroxide orpotassium hydroxide or ammonium hydroxide solution, until the pH levelis high, such as above pH 8.0 or above pH 9.0 or above pH 10.0. To thisalkaline solution of dissolved Lithol Rubine colorant can be optionallyadded a surface active agent as described previously, in particularembodiments surface active agent such as rosin soaps, delivered as anaqueous solution in the amount ranging from 0.1 wt % to 20 wt % based oncolorant solids, such as in an amount ranging from 0.5 wt % to about 10wt %, or in an amount ranging from 1.0 wt % to about 8.0 wt % based oncolorant solids, but the amount used can also be outside of theseranges.

In embodiments, the preparation of ultrafine and nanosized particles ofthe monoazo laked Pigment Red 57:1 was only enabled by the additionaluse of a sterically bulky stabilizer compound having a functional groupthat could non-covalently bond to the complementary functional moiety ofthe pigment as well as branched aliphatic functional groups that couldprovide steric bulk to the pigment particle surface. In embodiments,particularly suitable sterically bulky stabilizer compounds are branchedhydrocarbons with either carboxylate or sulfonate functional groups,compounds such as di[2-ethylhexyl]-3-sulfosuccinate sodium or sodium2-hexyldecanoate, and the like. The stabilizer compound is introduced asa solution or suspension in a liquid that is predominantly aqueous butmay optionally contain a water-miscible organic solvent such as THF,iso-propanol, NMP, Dowanol and the like, to aid dissolution of thestabilizer compound, in an amount relative to colorant moles rangingfrom about 5 mole-percent to about 100 mole-percent, such as from about20 mole-percent to about 80 mole-percent, or from about 30 mole-percentto about 70 mole-percent, but the concentrations used can also beoutside these ranges and in large excess relative to moles of colorant.

Lastly, the metal cation salt is added to transform the pigmentprecursor (Lithol Rubine-potassium salt in embodiments) into the desiredmonoazo laked pigment (Pigment Red 57:1 in embodiments), precipitated asnano-sized pigment particles. The aqueous solution of metal salt(calcium chloride in embodiments) with concentration ranging anywherefrom 0.1 mol/L to about 2 mol/L, is slowly added dropwise in nearlystoichiometric quantities such as amounts ranging from 1.0 molarequivalents relative to about 2.0 molar equivalents, or from 1.1 toabout 1.5 molar equivalents, or from 1.2 to about 1.4 molar equivalentsrelative to moles of colorant, however the amounts used can also beoutside of these ranges and in large excess.

The type of metal salt can have an impact on the extent of formingnano-sized pigment particles of monoazo laked pigments, in particularthe type of ligand that is coordinated to the metal cation and therelative ease with which it is displaced by a competing ligand fromeither the pigment functional moiety or the complementary functionalmoiety of the stabilizer compound, or both. In embodiments for monoazolaked Pigment Red 57:1, the nano-sized particles are formed usingcalcium (II) salts with ligands such as chloride, sulfate, acetate, andhydroxide; however a particularly desirable metal salt is calciumchloride for fastest reactivity.

The rates of addition of metal salt solution can also vary. For example,the slower the rate of addition, the more controlled is the rate ofpigment crystal formation and particle aggregation, and therefore thesmaller in size the pigment particles become.

Also important is the agitation rate and mixing pattern as the pigmentformation/precipitation step is occurring. The higher the agitation rateand the more dynamic or complex is the mixing pattern (i.e. with bafflesto prevent dead mixing zones), the smaller is the average particlediameter and the more narrow is the particle size distribution, asobservable by Transmission Electron Microscopy (TEM) imaging. Agitationcan be made more effective by using high-shear mixers such ashomogenizers, attritors, our even the use of ultrasonic probes.

Temperature during the pigment precipitation step using the metal saltsolution is also important. In embodiments, lower temperatures aredesired, such as from about 10° C. to about 50° C., or from about 15° C.to about 30° C., but the temperature can also be outside of theseranges.

In embodiments, the slurry of pigment nanoparticles is not treated norprocessed any further, such as performing additional heating which isoften practiced by pigment manufacturers, but instead is isolated byvacuum filtration or centrifugal separation processes. The pigmentsolids can be washed copiously with deionized water to remove excesssalts or additives that are not tightly associated or bonded with thepigment particle surface. The pigment solids can be dried byfreeze-drying under high vacuum, or alternatively, they can bepre-rinsed with a water-miscible solvent such as isopropanol oracetonitrile to remove excess water and then vacuum-oven dried. Theresulting nano-size pigment particles are generally non-aggregated andof high quality, which when imaged by TEM (Transmission ElectronMicroscopy), exhibit primary pigment particles and small aggregatesranging in diameters from about 10 nm to about 300 nm, and predominantlyfrom about 50 nm to about 150 nm. (Here, it is noted that averageparticle size d₅₀ or Z-average, and GSD particle size distributions aremeasured by Dynamic Light Scattering, an optical measurement techniquethat estimates the hydrodynamic radius of non-spherical pigmentparticles gyrating and translating in a liquid dispersion via Brownianmotion, by measuring the intensity of the incident light scattered fromthe moving particles. As such, the d₅₀ or the Z-average particle sizemetric obtained by DLS technique is always a larger number than theactual particle diameters observed by TEM imaging.)

Characterization of the chemical composition of washed and driednano-sized pigment particles are performed by NMR spectroscopy andelemental analysis. In embodiments, the composition of the monoazo lakedpigment Red 57:1 indicated that the nano-sized particles prepared by themethods described above, particularly when usingdi[2-ethylhexyl]-3-sulfosuccinate sodium as the sterically bulkystabilizer, retained at least 80% of the sterically bulky stabilizerthat was loaded into the process of making the nanoparticles, even aftercopious washing with deionized water to remove excess salts. Solid state¹H— and ¹³C-NMR spectroscopic analyses indicated that the stericstabilizer compound was associated non-covalently with the pigment as acalcium salt, and the chemical structure of the pigment adopted thehydrazone tautomer form, as shown in Figure below.

Pigment particles of monoazo laked pigments such as PR 57:1 that havesmaller particle sizes could also be prepared by the above two-stepmethod in the absence of using sterically bulky stabilizers and with theuse of surface active agents alone (for example, only rosin-type surfaceagents), depending on the concentrations and process conditionsemployed, but the pigment product did not predominantly exhibitnano-sized particles nor did the particles exhibit regular morphologies.In the absence of using the sterically bulky stabilizer compound, thetwo-step method described above typically produced rod-like particleaggregates, ranging in average particle diameter from 200-700 nm andwith wide particle distribution, and such particles were difficult todisperse into a polymer coating matrix and generally gave poorcoloristic properties. In embodiments, the combined use of a suitablesterically bulky stabilizer compound, such as branched alkanesulfonatesor alkylcarboxylates, with a minor amount of suitable surface activeagent such as derivatives of rosin-type surfactants, using either of thesynthesis methods described previously would afford the smallest finepigment particles having nanometer-scale diameters, more narrow particlesize distribution, and low aspect ratio. Various combinations of thesecompounds, in addition to variations with process parameters such asstoichiometry of reactants, concentration, addition rate, temperature,agitation rate, reaction time, and post-reaction product recoveryprocesses, enables the formation of pigment particles with tunableaverage particle size (d₅₀ or Z-average) from nanoscale sizes (about 1to about 100 nm) to mesoscale sizes (about 100 to about 500 nm) orlarger.

The advantages of this process include the ability to tune particle sizeand composition for the intended end-use application of the monoazolaked pigment, such as for use in toners and inks and coatings, whichfor example include phase-change, gel-based and radiation-curable inks,solid and non-polar liquid inks, solvent-based inks and aqueous inks andink dispersions. For the end-use application in piezoelectric inkjetprinting, nano-sized particles are advantageous to ensure reliableinkjet printing and prevent blockage of jets due to pigment particleagglomeration. In addition, nano-sized pigment particles areadvantageous for offering enhanced color properties in printed images,since in embodiments the color properties of nano-sized particles ofmonoazo laked pigment Red 57:1 were tunable with particle size. It wasobserved that as average particle size was decreased to thenanometer-scale, the hue angles were shifted from yellowish-red hues tobluish-red hues by an amount ranging from about 5 to about 35° in thecolor gamut space.

In embodiments, the nanosized pigment particles that were obtained formonoazo laked pigments can range in average particle size, d₅₀ orZ-average, or the average particle diameter, from about 10 nm to about250 nm or about 500 nm, such as from about 25 nm to about 175 nm, orfrom about 50 nm to about 150 nm, as measured by either dynamic lightscattering method or from TEM images. The pigment average particle sizecan accordingly be tuned by the above method, to provide compositionswith desired average particle sizes. For example, within the broadsuitable size range of about 1 nm to about 500 nm or larger, the pigmentcomposition can be provided to have an average particle size that isgenerally in the nanoscale size range (about 1 to about 100 nm) orgenerally in the mesoscale size range (about 100 to about 500 nm) orlarger. In embodiments, the pigment composition can be provided to havean average particle size in the ranges of from about 10 nm to about 50nm, about 50 nm to about 100 nm, about 100 nm to about 150 nm, or about150 nm to about 300 nm. For example, in embodiments, the pigmentcomposition can be provided to have an average particle size of about 50nm to about 12550 nm. In embodiments, the particle size distributionscan range such that the geometric standard deviation can range fromabout 1.1 to about 1.9, or from about 1.2 to about 1.7, as measured bydynamic light scattering method. The shape of the nanosized pigmentparticles can be one or more of several morphologies, including rods,platelets, needles, prisms or nearly spherical, and the aspect ratio ofthe nanosize pigment particles can range from about 1:1 to about 10:1,such as having aspect ratio between about 1:1 and about 5:1; however theactual metric can lie outside of these ranges.

In addition, nanosized pigment particles are advantageous for offeringenhanced color properties in printed images, since in embodiments thecolor properties of nanosized particles of monoazo laked pigment Red57:1 were tunable with particle size. In embodiments is disclosed thecoloristic properties (hue angle, a*, b*, and NLSI as measure ofspecular reflectivity) of nanosized pigment particles, particularly ofmonoazo laked red pigment, that are directly correlated and tunable withthe average pigment particle size, measured by either Dynamic LightScattering or electron microscopy imaging techniques, as well as pigmentcomposition with the non-covalently associated stabilizer, the latterwhich enables the control of particle size during pigment synthesis, andalso enables enhanced dispersability within certain polymer binders forcoating or other applications. For example, as average particle size wasdecreased to nanometer-scale, the hue angles were shifted fromyellowish-red hues to bluish-red hues by an amount ranging from about 5to about 35° in the color gamut space. The color of the nanosizedpigment particles have the same general hue as is found with largerpigment particles. However, in embodiments, is disclosed coloristicproperties of thin coatings of the nano-sized pigment particles of redmonoazo laked pigments dispersed in a polymer binder (such as ofpoly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate)), that exhibited asignificant shift to lower hue angle and lower b* values that revealedmore bluish magenta hues, and having either no change or a smallenhancement of a* value. In embodiments, any suitable polymer can beused to effect both good pigment dispersion and to act as a pigmentbinder to allow a good film forming quality about the substrate. Inother embodiments, it is advantageous when assessing coloristicproperties of pigments, as they are dispersed in coatings, for example,that the polymer used to disperse a pigment is transparent to visiblelight, either chemically or by way of not scattering light owing to thepolymer being more amorphous than crystalline, not be prone tofluorescence, and does not discolor during a dispersion making processor during the drying process after it has been coated on a substrate.

In embodiments, the hue angles of the coatings dispersed with thenanosized particles of monoazo laked pigment such as Pigment Red 57:1measured in the range from about 345° to about 5° on the 2-dimensionalb* a* color gamut space, as compared with hue angles ranging from about0° to about 20° for similarly prepared polymer coatings dispersed withconventional larger sized particles of Pigment Red 57:1. The coatingsdispersed with the nanosized particles of monoazo laked pigment canaccordingly exhibit hue angles of from about 345° to about 5°, such asfrom about 345° to about 0°, or from about 345° to about 350° or toabout 355°, on the 2-dimensional b* a* color gamut space.

Additionally, the specular reflectivity of the coatings of the nanosizedmonoazo laked red pigment was significantly enhanced from coatingsproduced with conventional larger sized pigment particles, which is anindicator of having very small particles being well-dispersed within thecoating. Specular reflectivity was quantified as the degree of lightscattering for the pigmented coating, a property that is dependent onthe size and shape distributions of the pigment particles and theirrelative dispersability within the coating binder. The Normalized LightScatter Index (NLSI) was quantified by measuring the spectral absorbanceof the coating, using a Shimadzu UV-160 spectrophotometer, in a regionwhere there is no absorbance from the chromogen of the monoazo lakedpigment, but only absorbance due to light scattered from largeaggregates and/or agglomerated pigment particles dispersed in thecoating binder. The light scattering absorbance data is then normalizedto a lambda-max optical density of 1.5, resulting in the NLSI value, inorder to directly compare the light scattering indices of severalpigmented coatings. The lower is the NLSI value, the smaller is thepigment particle size within the dispersed coating matrix. Inembodiments, the NLSI value of the nanosized monoazo laked red pigmentscan range from about 0.1 to about 3.0, such as from about 0.1 to about1.0. In comparison, the NLSI values observed with similarly preparedcoatings containing conventional larger sized monoazo laked red pigmentsrange anywhere from about 3.0 to about 75 (which indicates a very poorlydispersed coating).

The formed nanoscale pigment particle compositions can be used, forexample, as coloring agents in a variety of compositions, such as inliquid (aqueous or non-aqueous) ink vehicles, including inks used inconventional pens, markers, and the like, liquid ink jet inkcompositions, solid or phase change ink compositions, and the like. Forexample, the colored nanoparticles can be formulated into a variety ofink vehicles, including “low energy” solid inks with melt temperaturesof about 60 to about 130° C., and solvent-based liquid inks orradiation-curable such as UV-curable liquid inks comprised ofalkyloxylated monomers, and even aqueous inks.

In addition to ink compositions, the nanoscale-sized pigment compositioncan be used in a variety of other applications, where it is desired toprovide a specific color to the composition. For example, thenanoscale-sized pigment composition can also be used in the same manneras conventional pigments in such uses as colorants for paints, resins,lenses, filters, printing inks, and the like according to applicationsthereof. By way of example only, the nanoscale-sized pigment compositionof embodiments can be used for toner compositions, which include polymerparticles and nanoscale pigment particles, along with other optionaladditives, that are formed into toner particles and optionally treatedwith internal or external additives such as flow aids, charge controlagents, charge-enhancing agents, filler particles, radiation-curableagents or particles, surface release agents, and the like.

An example is set forth herein below and is illustrative of differentcompositions and conditions that can be utilized in practicing thedisclosure. All proportions are by weight unless otherwise indicated. Itwill be apparent, however, that the disclosure can be practiced withmany types of compositions and can have many different uses inaccordance with the disclosure above and as pointed out hereinafter.

EXAMPLES

Examples of Monoazo Laked Red Pigment Compositions and Methods of Makingin Various Particle Sizes:

Comparative Example 1 Synthesis of Pigment Red 57:1 particles using atwo-step method

Step 1: Diazotization and Couing: Into a 500 mL round bottom flaskequipped with a mechanical stirrer, thermometer, and addition funnel wasdissolved 2-amino-5-methylbenzenesulfonic acid (8.82 g) into 0.5M KOHaqueous solution (97.0 mL). The resulting brown solution was cooled to0° C. A 20 wt % aqueous solution of sodium nitrite (NaNO₂; 3.28 gdissolved into 25 mL water) was added slowly to the first solution whilemaintaining the temperature below 3° C. To the red-brown homogeneousmixture was added dropwise concentrated HCl (10M, 14.15 mL) over 1 hour,maintaining the internal temperature below 2° C. The mixture formed apale brown suspension, and following complete addition of conc. HCl, thesuspension was stirred an additional 30 min.

In a separate 2-L resin kettle was dissolved 3-hydroxy-2-naphthoic acid(8.86 g) into an aqueous solution of KOH (8.72 g) in water (100 mL). Anadditional 250 mL of water was added, and the light-brown solution wasthen cooled to 15° C. while stirring vigorously. The cold suspension ofthe diazonium salt suspension was then added slowly to the couplingsolution while mixing vigorously. The color changed initially to a darkred solution, and ultimately to a yellowish-red (orange) slurry ofprecipitated dyestuff. The mixture was stirred for 2 hours while warmingup to room temp, then filtered and diluted with about 500 mL ofdeionized water to produce an orange aqueous slurry of LitholRubine-Potassium salt dye (a synthetic precursor of Pigment Red 57:1)having solids content of about 1.6 wt %.

Step 2: Laking Step to Produce Pigment Red 57:1 Particles

Into a 500 mL round bottom flask equipped with mechanical stirrer andcondenser was charged 126 g of aqueous slurry of Lithol Rubine-Potassiumsalt dye precursor from above having about 1.6% wt solids content. ThepH of the slurry was adjusted to at least 9.0 or higher by addition of0.5 M KOH solution, after which the dyestuff was fully dissolved. Anaqueous solution of calcium chloride dihydrate (0.5 M solution, 13 mL)was added dropwise to the slurry while stirring vigorously. A redprecipitate formed immediately, and after addition was completed, theslurry was stirred for an additional 1 hour. The red slurry was thenheated to about 75° C. for 20 min, then cooled to room temp. The slurrywas filtered under high vacuum through a 1.2 μm acrylic polymermembrane, then reslurried twice with 200 mL portions of deionized water.The pH and conductivity of the filtrates after each filtration weremeasured and recorded, with the final wash filtrate having nearlyneutral pH of 6.2 and conductivity of about 13.5 μS/cm, indicating lowresidual salts. The red pigment filtercake was reslurried into about 200mL of DIW and freeze-dried for 48 hours, to afford a red colored powder(1.95 grams). TEM microscopy revealed long rod-like particles andaggregates, with particle diameters ranging from about 200 nm to about700 nm, and large aspect ratios ranging from about 4:1 to about 10:1.

Example 1 Synthesis of Nano-Sized Particles of Pigment Red 57:1 by aTwo-Step Method

Step 1: Diazotization and Coupling: Into a 500 mL round bottom flaskequipped with a mechanical stirrer, thermometer, and addition funnel wasdissolved 2-amino-5-methylbenzenesulfonic acid (8.82 g) into 0.5M KOHaqueous solution (97.0 mL). The resulting brown solution was cooled to0° C. A 20 wt % aqueous solution of sodium nitrite (NaNO₂; 3.28 gdissolved into 25 mL water) was added slowly to the first solution whilemaintaining the temperature below 3° C. To the red-brown homogeneousmixture was added dropwise concentrated HCl (10M, 14.15 mL) over 1 hour,maintaining the internal temperature below 2° C. The mixture formed apale brown suspension, and following complete addition of conc. HCl, thesuspension was stirred an additional 30 min.

In a separate 2-L resin kettle was dissolved 3-hydroxy-2-naphthoic acid(8.86 g) into an aqueous solution of KOH (8.72 g) in water (100 mL). Anadditional 250 mL of water was added, and the light-brown solution wasthen cooled to 15° C. while stirring vigorously. The cold suspension ofthe diazonium salt suspension was then added slowly to the couplingsolution while mixing vigorously. The color changed immediately to adark red solution, and ultimately to a yellowish-red (orange) slurry ofprecipitated dyestuff. The mixture was stirred for 2 hours while warmingup to room temp, then filtered and reslurried with about 500 mL ofdeionized water to produce an orange aqueous slurry of LitholRubine-Potassium salt dye having solids content of about 1.6 wt %.

Step 2: Laking Step to Produce Pigment Red 57:1 Particles:

Into a 500 mL round bottom flask equipped with mechanical stirrer andcondenser was charged 126 g of aqueous slurry of Lithol Rubine-Potassiumsalt dye from above (Example 1, Step 1) having about 1.6% wt solidscontent. The pH of the slurry was adjusted to at least 9.0 or higher byaddition of 0.5 M KOH solution, after which the dyestuff was fullydissolved. An aqueous solution 5 wt % Dresinate X (4.0 mL) was added,followed by a solution containing sodium dioctyl sulfosuccinate (0.96 g)dissolved in 100 mL of 90:10 deionized water/THF mixture. No visiblechange was observed. An aqueous solution of calcium chloride dihydrate(0.5 M solution, 13 mL) was added dropwise to the slurry while stirringvigorously. A red precipitate formed immediately, and after completeaddition of the calcium chloride solution, the slurry was stirred for anadditional 1 hour. The red slurry was then heated to about 75° C. for 20min, then cooled to room temp. The slurry was filtered under high vacuumthrough a 0.45 μm Nylon membrane cloth, then reslurried twice with 75 mLportions of DIW. The pH and conductivity of the final wash filtrate was7.4 and about 110 μS/cm, respectively, indicating that residual acidsand salt by-products were removed. The red pigment filtercake wasreslurried in about 250 mL of DIW and freeze-dried for 48 hours toafford a dark red colored powder (2.65 grams). Transmission electronmicroscopy images of the powder revealed platelet-like particles withparticle diameters ranging from 30-150 nm, and aspect ratios that wereless than 3:1. ¹H-NMR spectroscopy analysis (300 MHz, DMSO-d₆) of thepigment indicated that the pigment adopted the hydrazone tautomer form,and that the dioctyl sulfosuccinate stabilizer compound was present atapproximately 40 mol % (representing about 80% remaining of actualloading) and was associated with a calcium cation (determined by ICPspectroscopy).

Example 2 Synthesis of Nano-Sized Particles of Pigment Red 57:1 by aTwo-Step Method

The procedure of Step 1 of Example 1 above was reproduced. Step 2:Laking

Into a 500 mL round bottom flask equipped with mechanical stirrer andcondenser was charged 126 g of aqueous slurry of Lithol Rubine-Potassiumsalt dye from above (Example 1) having about 1.6% wt solids content. ThepH of the slurry was adjusted to at least 9.0 or higher by addition of0.5 M KOH solution, after which the dyestuff was fully dissolved. Anaqueous solution 5 wt % Dresinate X (4.0 mL) was added, followed by asolution containing sodium dioctyl sulfosuccinate (0.96 g) dissolved in100 mL of 90:10 deionized water/THF mixture. No visible change wasobserved. An aqueous solution of calcium chloride dihydrate (0.5 Msolution, 13 mL) was added dropwise to the slurry while stirringvigorously. A red precipitate formed immediately, and after completeaddition of the calcium chloride solution, the slurry was stirred for anadditional 1 hour. The red slurry was then heated to about 75° C. for 20min, then cooled to room temp. The slurry was filtered under high vacuumthrough a 0.45 μm Nylon membrane cloth, then reslurried twice with 75 mLportions of DIW. The pH and conductivity of the final wash filtrate was7.15 and about 155 ES/cm, respectively. The red pigment filtercake wasreslurried in about 250 mL of DIW and freeze-dried for 48 hours toafford a dark red-colored powder (2.62 grams). Transmission electronmicroscopy images of the powder revealed platelet-like particles withparticle diameters ranging from 50-175 nm, and aspect ratios equal to orless than 3:1

Example 3 Synthesis of Nano-Sized Particles of Pigment Red 57:1 by aTwo-Step Method

Step 1: Diazotization and Coupling: Into a 500 mL round bottom flaskequipped with a mechanical stirrer, thermometer, and addition funnel wasdissolved 2-amino-5-methylbenzenesulfonic acid (12.15 g) into 0.5M KOHaqueous solution (135 mL). The resulting brown solution was cooled to 0°C. A 20 wt % aqueous solution of sodium nitrite (NaNO₂; 4.52 g dissolvedinto 30 mL water) was added slowly to the first solution whilemaintaining the temperature below −2° C. Concentrated HCl (10M, 19.5 mL)was then slowly added dropwise over 1 hour while maintaining theinternal temperature below 0° C. The mixture formed a pale brownsuspension and following complete addition of conc. HCl, the suspensionwas stirred an additional 30 min.

In a separate 2-L resin kettle was dissolved 3-hydroxy-2-naphthoic acid(12.2 g) into an aqueous solution of KOH (12.0 g) in water (130 mL). Anadditional 370 mL of water was added, and the pale brown solution wasthen cooled to about 15° C. while stirring. The cold suspension of thediazonium salt solution was then added slowly to the coupling solutionwhile mixing vigorously. The color change was immediate to darkblack-red solution, and ultimately to a yellowish-red (orange) slurry ofprecipitated dyestuff. The mixture was stirred for at least 2 hourswhile warming up to room temp, then filtered and reslurried with about600 mL of deionized water to produce an orange-colored slurry of LitholRubine-Potassium salt dye having solids content of about 3.75%-wt.

Step 2: Laking Step to Produced Nano-Sized Particles of Pigment Red 57:1

Into a 1-L resin kettle equipped with mechanical stirrer and condenserwas charged 265 g of aqueous slurry of Lithol Rubine-Potassium salt dyeprepared from Step 1 of Example 2 above, having approximately 3.75%-wtsolids content). The pH of the slurry was adjusted to at least 9.0 orhigher by addition of 0.5 M KOH solution, after which the dyestuff wasfully dissolved. An aqueous solution 5 wt % Dresinate X (20.0 mL) wasadded while stirring, followed by a solution containing sodium dioctylsulfosuccinate (4.8 g) dissolved in 220 mL of 90:10 deionized water/THFmixture was slowly added to the mixture with stirring. An aqueoussolution of calcium chloride dihydrate (0.5 M solution, 65 mL) was addeddropwise to the slurry while stirring vigorously. A red precipitateformed immediately, and after complete addition of the calcium chloridesolution, the slurry was stirred for an additional 1 hour. The redslurry was then heated to about 60° C. for 30 min, then cooledimmediately in a cold water bath. The slurry was filtered under highvacuum through a 0.8 micron Versapor membrane cloth (obtained from PALLCorp.), then reslurried twice with about 750 mL portions of DIW, andfiltered once more. The pH and conductivity of the final wash filtratewas 7.5 and about 208 μS/cm, respectively. The red pigment filtercakewas reslurried in about 600 mL of deionized water and freeze-dried for48 hours, to afford a dark red-colored powder (12.75 grams).Transmission electron microscopy images of the powder revealedpredominantly platelet-like particles with particle diameters rangingfrom 50-150 nm, and aspect ratios that were equal to or less than about3:1

Example 4 Preparation of Nano-Sized Particles of Pigment Red 57:1 Usingthe Two-Step Method

Into a 250 mL round bottom flask equipped with mechanical stirrer andcondenser was charged 10 g of aqueous slurry of Lithol Rubine-Potassiumsalt dye precursor prepared as in Step 1 of Example 3, except that thesolids concentration in the aqueous slurry was about 10.0 wt %. The pHof the slurry was adjusted to at least 9.0 or higher by addition of 0.5M KOH solution, after which the dyestuff was fully dissolved. An aqueoussolution 5 wt % Dresinate X (1.0 mL) was added, followed by a 0.05 mol/Lsolution (34.5 mL) containing sodium dioctyl sulfosuccinate dissolved in90:10 deionized water/THF. No visible change was observed. An aqueoussolution of calcium chloride dihydrate (1.0 M solution, 2.15 mL) wasadded dropwise by syringe pump to the slurry while stirring vigorously.A red precipitate formed immediately, and then the slurry was stirred atroom temperature for an additional 30 min. The red slurry was thenfiltered under high vacuum through a 0.8 μm Versapor membrane cloth(obtained from PALL Corp.), then reslurried twice with 50 mL portions ofdeionized water and filtered each time after reslurrying. The pH andconductivity of the final wash filtrate was 7.5 and about 135 μS/cm,respectively, indicating that residual acids and salt by-products wereremoved. The red pigment filtercake was reslurried in about 30 mL ofdeionized water and freeze-dried for 48 hours to afford a dark redcolored powder (1.32 grams). Transmission electron microscopy images ofthe powder revealed very small platelet-like particles with particlediameters ranging from 50 to 175 nm, and aspect ratios were equal to orless than about 3:1. Dynamic Light Scattering analysis measured anaverage particle size, d₅₀, of 189 nm and GSD of 1.54 (Z-averageparticle size of 176 nm; polydispersity index, PDI, of 0.143). ¹H-NMRspectroscopy analysis (300 MHz, DMSO-d₆) of the material indicated thatthe pigment adopted the hydrazone tautomer form, and that the dioctylsulfosuccinate stabilizer compound was present at a level ranging fromapproximately 50-75 mol %.

Example 5 Preparation of Small Particles of Pigment Red 57:1 Using theTwo-Step Method

Into a 500 mL round bottom flask equipped with mechanical stirrer andcondenser was charged 126 g of aqueous slurry of Lithol Rubine-Potassiumsalt dye precursor (prepared as in Step 1 of Example 1) having about1.6% wt solids content. The pH of the slurry was adjusted to at least9.0 or higher by addition of 0.5 M KOH solution, after which thedyestuff was fully dissolved. An aqueous solution 5 wt % Dresinate X(4.0 mL) was added, followed by a solution containing sodium dioctylsulfosuccinate (1.92 g) dissolved in 100 mL of 90:10 deionized water/THFmixture. No visible change was observed. An aqueous solution of calciumchloride dihydrate (0.5 M solution, 13 mL) was added dropwise to theslurry while stirring vigorously. A red precipitate formed immediately,and after complete addition of the calcium chloride solution, the slurrywas stirred for an additional 1 hour. The red slurry was then heated toabout 75° C. for 20 min, then cooled to room temp. The slurry wasfiltered under high vacuum through a 0.45 μm Nylon membrane cloth, thenreslurried twice with 75 mL portions of DIW. The pH and conductivity ofthe final wash filtrate was 7.75 and conductivity of about 500 μS/cm.The red pigment filtercake was reslurried in about 250 mL of DIW andfreeze-dried for 48 hours to afford a dark red-colored powder (2.73grams). Transmission electron microscopy images of the powder showed adistribution of particle sizes, with diameter ranging from 50 to 400 nmand having particle morphologies that were predominantly platelets.

Example 6 Preparation of Small Particles of Pigment Red 57:1 Using aTwo-Step Method

The sterically bulky stabilizer compound used was potassium salt of2-hexyldecanoic acid, prepared by treatment of 2-hexyldecanoic acid withpotassium hydroxide dissolved in THF, after which the THF solvent wasremoved. Into a 500-mL round-bottom flask equipped with condenser andmechanical stirrer was charged 126 g of aqueous slurry of LitholRubine-Potassium salt (prepared as in Step 1 of Example 1) having about1.6% wt solids content. The pH of the slurry was adjusted to at least9.0 or higher by addition of 0.5 M KOH solution, after which thedyestuff was fully dissolved. An aqueous solution 5 wt % Dresinate X(4.0 mL) was added, followed by a solution containing potassium2-hexyldecanoate (1.28 g) dissolved in 100 mL of 80:20 deionizedwater/THF mixture, added dropwise while stirring vigorously. An aqueoussolution of calcium chloride dihydrate (0.5 M solution, 13 mL) was addedto the slurry while stirring vigorously causing a bluish-red pigmentprecipitate to form. The slurry was stirred for 1 hour, heated to about75° C. for 20 min, then cooled to room temperature. The slurry wasfiltered under high vacuum through a 0.8 μm Nylon membrane cloth, thenreslurried once with 150 mL of DIW and filtered again. The pH andconductivity of the final wash filtrate was pH 8.38 and conductivity ofabout 63 μS/cm. The red pigment 57:1 filtercake was reslurried intoabout 150 mL of DIW and freeze-dried for 48 hours to afford a red powder(2.95 grams). TEM micrograph images showed a distribution of particlesizes, with diameters ranging from 50 to about 400 nm and havingparticle morphologies that included platelets as well as rods.

Example 7 Preparation of Pigment Red 57:1 Particles Using the Two-StepMethod

Into a 250 mL round bottom flask equipped with mechanical stirrer andcondenser was charged 25 g of aqueous slurry of Lithol Rubine-Potassiumsalt dye precursor prepared as in Step 1 of Example 3, except that thesolids concentration in the aqueous slurry was about 4.0 wt %. The pH ofthe slurry was adjusted to at least 9.0 or higher by addition of 0.5 MKOH solution, after which the dyestuff was fully dissolved. An aqueoussolution of 5 wt % Dresinate X (1.0 mL) was added, followed by a 0.05mol/L solution (11 mL) containing sodium dioctyl sulfosuccinatedissolved in 90:10 deionized water/THF. No visible change was observed.An aqueous solution of calcium chloride dihydrate (0.5 M solution, 6.5mL) was added dropwise by syringe pump to the slurry while stirringvigorously. A red precipitate formed immediately, and then the slurrywas stirred at room temperature for an additional 30 min. The red slurrywas then filtered under high vacuum through a 0.8 μm Versapor membranecloth (obtained from PALL Corp.), then reslurried twice with 50 mLportions of deionized water and filtered each time after reslurrying.The pH and conductivity of the final wash filtrate was 6.7 and about22.5 μS/cm, respectively, indicating that residual acids and saltby-products were removed. The red pigment filtercake was reslurried inabout 30 mL of deionized water and freeze-dried for 48 hours to afford adark red colored powder (0.92 grams). Transmission electron microscopyimages of the powder revealed irregular rod-like particles with particlediameters ranging from 100-600 nm with the majority of particles lessthan about 300 nm, and aspect ratios of greater than about 4:1. DynamicLight Scattering analysis measured an average particle size, d₅₀, of 259nm and GSD of 1.60 (Z-average particle size of 224 nm; polydispersityindex, PDI, of 0.145).

Example 8 Preparation of Pigment Red 57:1 Particles Using the Two-StepMethod

Into a 250 mL round bottom flask equipped with mechanical stirrer andcondenser was charged 25 g of aqueous slurry of Lithol Rubine-Potassiumsalt dye precursor prepared as in Step 1 of Example 3, except that thesolids concentration in the aqueous slurry was about 4.0 wt %. The pH ofthe slurry was adjusted to at least 9.0 or higher by addition of 0.5 MKOH solution, after which the dyestuff was fully dissolved. An aqueoussolution of 5 wt % Dresinate X (4.0 mL) was added, followed by a 0.25mol/L solution (2 mL) containing sodium dioctyl sulfosuccinate dissolvedin 90:10 deionized water/THF. No visible change was observed. An aqueoussolution of calcium chloride dihydrate (1.0 M solution, 2 mL) was addeddropwise by syringe pump to the slurry while stirring vigorously. A redprecipitate formed immediately, and then the slurry was stirred at roomtemperature for an additional 30 min. The red slurry was then filteredunder high vacuum through a 0.8 μm Versapor membrane cloth (obtainedfrom PALL Corp.), then reslurried twice with 50 mL portions of deionizedwater and filtered each time after reslurrying. The pH and conductivityof the final wash filtrate was 6.9 and about 75.4 μS/cm, respectively,indicating that residual acids and salt by-products were removed. Thered pigment filtercake was reslurried in about 30 mL of deionized waterand freeze-dried for 48 hours to afford a dark red colored powder (0.70grams). Transmission electron microscopy images of the powder revealedlarge rod-like particles with particle diameters ranging from 180-900 nmwith the majority of particles less than about 400 nm, and aspect ratiosof greater than about 4:1. Dynamic Light Scattering analysis measured anaverage particle size, d₅₀, of 269 nm and GSD of 1.64 (Z-averageparticle size of 252 nm; polydispersity index, PDI, of 0.185).

Example 9 Preparation of Pigment Red 57:1 Particles Using the Two-StepMethod

Into a 250 mL round bottom flask equipped with mechanical stirrer andcondenser was charged 25 g of aqueous slurry of Lithol Rubine-Potassiumsalt dye precursor prepared as in Step 1 of Example 3, except that thesolids concentration in the aqueous slurry was about 4.0 wt %. The pH ofthe slurry was adjusted to at least 9.0 or higher by addition of 0.5 MKOH solution, after which the dyestuff was fully dissolved. An aqueoussolution of 5 wt % Dresinate X (4.0 mL) was added, followed by a 0.05mol/L solution (34.5 mL) containing sodium dioctyl sulfosuccinatedissolved in 90:10 deionized water/THF. No visible change was observed.An aqueous solution of calcium chloride dihydrate (1.0 M solution, 2 mL)was added dropwise by syringe pump to the slurry while stirringvigorously. A red precipitate formed immediately, and then the slurrywas stirred at room temperature for an additional 30 min. The red slurrywas then filtered under high vacuum through a 0.8 μm Versapor membranecloth (obtained from PALL Corp.), then reslurried twice with 50 mLportions of deionized water and filtered each time after reslurrying.The pH and conductivity of the final wash filtrate was 6.8 and about 77μS/cm, respectively, indicating that residual acids and salt by-productswere removed. The red pigment filtercake was reslurried in about 30 mLof deionized water and freeze-dried for 48 hours to afford a dark redcolored powder (0.62 grams). Transmission electron microscopy images ofthe powder revealed platelets as well as rod-like particles withparticle diameters ranging from 100-400 nm with the majority ofparticles less than about 250 nm, and aspect ratios of less than about4:1. Dynamic Light Scattering analysis measured an average particlesize, d₅₀, of 235 nm and GSD of 1.61 (Z-average particle size of 224 nm;polydispersity index, PDI, of 0.152).

Example 10 Preparation of Small Particles of Pigment Red 57:1 Using theTwo-Step Method

Into a 250 mL round bottom flask equipped with mechanical stirrer andcondenser was charged 10 g of aqueous slurry of Lithol Rubine-Potassiumsalt dye precursor prepared as in Step 1 of Example 3, except that thesolids concentration in the aqueous slurry was about 10.0 wt %. The pHof the slurry was adjusted to at least 9.0 or higher by addition of 0.5M KOH solution, after which the dyestuff was fully dissolved. An aqueoussolution of 5 wt % Dresinate X (4.0 mL) was added, followed by a 0.05mol/L solution (11 mL) containing sodium dioctyl sulfosuccinatedissolved in 90:10 deionized water/THF. No visible change was observed.An aqueous solution of calcium chloride dihydrate (1.0 M solution, 3.25mL) was added dropwise by syringe pump to the slurry while stirringvigorously. A red precipitate formed immediately, and then the slurrywas stirred at room temperature for an additional 30 min. The red slurrywas then filtered under high vacuum through a 0.8 μm Versapor membranecloth (obtained from PALL Corp.), then reslurried twice with 50 mLportions of deionized water and filtered each time after reslurrying.The pH and conductivity of the final wash filtrate was 7.5 and about42.7 μS/cm, respectively, indicating that residual acids and saltby-products were removed. The red pigment filtercake was reslurried inabout 30 mL of deionized water and freeze-dried for 48 hours to afford adark red colored powder (0.61 grams). Transmission electron microscopyimages of the powder revealed platelets as well as rod-like particleswith particle diameters ranging from 75 nm to about 300 nm with themajority of particles less than about 200 nm, and aspect ratios of lessthan about 3:1. Dynamic Light Scattering analysis measured an averageparticle size, d₅₀, of 209 nm and GSD of 1.57 (Z-average particle sizeof 193 nm; polydispersity index, PDI, of 0.148).

Examples of Liquid Dispersions containing Monoazo Laked PigmentParticles (Including Nano-Sized Particles) and Their ColoristicProperties

Example 11 Method for Preparation of Liquid Dispersions and of PolymerCoatings

A series of liquid, non-aqueous dispersions were prepared using apolymeric dispersant and the nano-sized PR 57:1 pigments from Examples1, 2, 3, 4, 5 and 6; the larger-sized pigment particles prepared asdescribed in the Comparative Example 1; as well as two commercialsources of PR 57:1 obtained from Clariant (lot #L7B01) and Aakash.Coatings on clear Mylar film were prepared from these liquiddispersions, and evaluated in the following manner: Into a 30 mL amberbottle was added 0.22 g of pigment, 0.094 g polyvinylbutyral (B30HHobtained from Hoescht), 7.13 g n-butyl acetate (glass-distilled grade,obtained from Calcdon Laboratories) and 70.0 g of ⅛″ stainless steelshot (Grade 25 440C obtained from Hoover Precision Products). Thebottles were transferred to a jar mill and were allowed to gently millfor 4 days at 100 RPM. Two draw-down coatings were obtained for eachdispersion using an 8-path gap on clear Mylar film such that the wetthicknesses for each coating comprised of PR 57:1 pigment sample were0.5 and 1 mil. The air-dried coatings on clear Mylar film were thendried in a horizontal forced-air oven at 100° C. for 20 minutes.

Example 12 Measurement of Pigment Particle Size by Dynamic LightScattering

The measurements of various example PR57:1 pigments' particle sizes wereperformed on a Malvern ZetaSizer HT at 25° C. Each of the pigmentdispersions prepared in Example 8 were diluted in a solution ofpolyvinylbutyral (B30HH obtained from Hoescht) in n-butyl acetate(glass-distilled grade, obtained from Calcdon Laboratories) andsonicated at low power for 1 minute. For each determination of particlesize and distribution, 3 replicates of 12 runs were performed whereinthe repeatability of particle size data was realized for each sample.The particle size data for the diluted samples that were prepared inExample 8 can be found in Table 10.

Example 13 Evaluation of Coatings prepared from Liquid PigmentDispersions

The coatings on clear Mylar film prepared as described in Example 11were assessed for coloristic and light scattering properties in thefollowing manner: The UVVIS/NIR transmittance spectra of each coatingwere obtained using a Shimadzu UV160 spectrophotometer, and the resultsshowed dramatically reduced light scattering and remarkable specularreflectivity for the nano-sized PR57:1 pigment samples described herein,compared with the spectra of coatings prepared with commercial PR57:1pigment samples obtained from Clariant and Aakash. The degree of lightscattering in a coating is dependent on both the size and shapedistributions of the pigment particles and their relative dispersabilitywithin the coating matrix, and the Normalized Light Scatter Index (NLSI)method was developed to be a measure of this characteristic for thepigmented coatings. NLSI is quantified by first measuring the spectralabsorbance of the coating in a region where there is no absorbance fromthe chromogen of the monoazo laked pigment (for PR57:1, a suitableregion is 700-900 nm), but only absorbance due to light scattered fromlarge aggregates and/or agglomerated pigment particles dispersed in thecoating binder. The Normalized Light Scatter Index (NLSI) is thenobtained by normalizing each of the samples' light scattering indices(from 700 to 900 nm) to a lambda-max optical density=1.5. In this way,the degree of light scattering for each pigmented coating could becompared directly against each other. The lower the NLSI value, thesmaller the inferred particle size of the dispersed pigment in thecoating. A relationship between decreasing average particle size anddecreasing NLSI value was found to exist with the coatings prepared fromthe example pigments shown in Table 8. In particular, the nano-sizedmonoazo laked pigment PR57:1 of Example 3 had by far the lowest degreeof light scattering, with an NLSI value of 0.3. The coloristicproperties of the Mylar coatings were determined using an X-RITE 938spectrodensitometer. L* a* b* and optical density (O.D.) values wereobtained for each of the samples, and the L* a* b* were normalized to anoptical density of 1.5, and used to calculate the hue angle and chroma(C*), as listed in Table 8.

TABLE 8 Normalized Light Scatter Indices (NLSI), Coloristic propertiesnormalized to O.D. = 1.5, Particle size ranges and Dispersionstabilities of example PR57:1 pigments Com- Clariant Aakash parativeExample Metric PR57:1 PR57:1 Example 1 1 2 3 4 5 6 7 8 9 10 L*^(a) 47.948.0 44.8 50.8 50.6 51.7 53.0 49.9 49.6 50.1 49.0 50.8 52.0 a*^(a) 71.171.2 71.5 76.5 77.2 79.4 78.8 76.7 73.6 76.4 74.7 77.2 77.7 b*^(a)  8.717.5 34.8 −16.4 −17.4 −18.8 −15.0 −18.9 1.4 −2.4 6.1 −5.8 −12.5 HueAngle  6.6 13.8 28.1 347.9 347.1 346.6 349.2 346.1 0.9 358.3 4.6 355.8350.9 (°)^(a) C*^(a) 72.6 73.4 78.1 78.6 77.5 81.3 80.5 78.9 73.9 78.276.7 78.9 79.9 Particle Size ~50 to ~50 to ~200 to ~30 to ~50 to ~50 to~50 to ~50 to ~50 to ~100 to ~180 to ~100 to ~75 to Diameter ~400 ~400~700 ~150 ~175 ~150 ~175 ~400 ~400 ~600; ~900; ~400; ~300; Range^(b)most most most most (nm) <300 nm <400 nm <250 nm <200 nm Normalized  5.59.9 74.1 0.3 1.3 1.0 0.7 0.9 4.8 1.8 2.2 1.5 0.4 Light Scatter Index^(a)Dispersion 2 days 2 days <1 day 6 3 3 3 6 2 3 3 3 3 Stability monthsmonths months months months months months months months months In Table8, ^(a) denotes that the various coloristic and light scatter indexmetrics were normalized to optical density of 1.5, and, ^(b) denotesthat the particle size diameter was determined by Transmission ElectronMicroscopy.

For the data in Table 9, the various coloristic properties, normalizedlight scatter indices, of the example pigments as they were dispersedand coated onto Clear Mylar® and the dispersion stabilities found inTable 8 have been organized into various ranges by way of the following:

a) ¹L*, where A denotes 49≦L*≦54, B denotes L*>54, C denotes L*<49,

b) ²a*, where A denotes a*≧78, B denotes 75≦a*<78, C denotes a*<75,

c) ³b*, where A denotes b*≦−18, B denotes −10≦b*<−18, C denotes−2≦b*<−10, D denotes 6≦b*<−2, E denotes b*>6,

d) ⁴NLSI, where A denotes NLSI≦1, B denotes 1<NLSI≦2, C denotes NLSI>2,and

e) ⁵Dispersion Stability at Room Temperature, where A denotes stability≧3 months, B denotes stability ≧1 week but <3 months, C denotesstability <1 week.

From table 9, it is clear that a variety of coloristic properties can berealized by adjusting the synthetic process of nano-sized PR57:1 to suitpigment compositions having relatively smaller particle sizes,relatively larger particle sizes or a combination of particle sizes tosuit the needs of a particular application. For example, it may usefulin a particular application, such as in ink formulations, to have theability to tune the coloristic properties of an ink, a magenta ink, forexample, without using excessive energy to grind down the pigmentparticles. The ability to control various properties of nano-sizedPR57:1, such as hue angle, as determined from its synthesis and work-uphistory, is beneficial to the environment as lower energy consumptionwould be required to process a dispersion or ink for a givenapplication, such as for coatings or ink jet inks, such as piezo inkjetinks.

TABLE 9 Ranged and Normalized Scatter Indices (NLSI), Coloristic andDispersion Stability Properties of example PR57:1 pigments, normalizedto O.D. = 1.5 Clariant Aakash Comparative Example Metric PR57:1 PR57:1Example 1 1 2 3 4 5 6 7 8 9 10 L*¹ C C C A A A A A A A A A A a*² C C C BB A A B C B C B B b*³ E E E B B A B A D C E C B Normalized Light C C C AB A A A C B C B A Scatter Index⁴ Dispersion C C C A A A A A A A A A AStability⁵

Example 14 b*a* Coloristic Properties of Coatings prepared from LiquidPigment Dispersions

The graphs in FIGS. 1 and 2 visually illustrate the significant shiftsin b* a* gamut observed with coatings prepared with the nano-sizedPR57:1 pigments from Examples 1, 2, 3, 4 and 5, in addition to theextended C* chroma for the nano-sized pigment examples. Furthermore, thegraph in FIG. 1 shows a clear blue-shifting of hue that directlycorresponds to decreasing particle size/particle diameters of theexample PR57:1 pigments, a relationship which is also inferred from theNormalized Light Scatter Index (NLSI) values of Table 8. (Note: For easeof generating the graph, the b* vertical axis shows “negative” hueangles, which represent the number of degrees <360 degrees.) The lightscattering and coloristic data accumulated provide evidence for theability to tune color properties and specular reflectivity of pigmentedcoatings with tunable particle size of surface-enhanced fine particlesof monoazo laked red pigments, in particular Pigment Red 57:1. This isachieved by using the methods of making such nano-sized pigments ofPR57:1 as described herein, in particular using the two-step processwhich uses sterically bulky stabilizer compounds to limit particleaggregation and thereby limit particle size as well as enhancedispersion and color characteristics of the nano-sized pigmentparticles. Furthermore, the ability to easily tune color properties ofsuch monoazo laked pigments provides a means to control the colorquality so that inexpensive azo laked pigments like PR57:1 can be usedto obtain magenta color that are normally exhibited by higher cost redpigments, such as the quinacridone-type Pigment Red 122 and Pigment Red202.

It can be seen from the data in FIG. 2 that there is a semi-logarithmiccorrelation between hue angle and Normalized Light Scatter Index (NLSI)of the example PR57:1 pigments, normalized to an optical density of 1.5.The relatively greater degree of blue-shifting of hue for some examplepigments, especially those made in Examples 1, 2, 3, 4, and 5 occurredwith correspondingly lower NLSI values. As well, red-shifting of hue forsome example pigments occurred with correspondingly higher NLSI values.Furthermore, the direct correlation between hue angle of examplepigments coated onto clear Mylar® (normalized to O.D.=1.5) and ofparticle size (prepared and measured as Z-average as disclosed inExample 9) as seen in FIG. 3 clearly indicate a range of hue angles(colors) suitable for various applications, such as inks or coatings.Thus various properties of example PR57:1 pigments can be easily,including pigment particle size and dispersed pigment hue, by adjustingcertain aspects of the PR57:1 composition and method of making,including, for example, reactant loading and stoichiometry, reactantsrate of addition and concentration, stirring speed, temperature andvarious pigment work up variances, including types and volumes ofpigment washes.

FIG. 4 shows the nearly linear correlation between NLSI and Z-averageparticle size indicating that the particle size distributions in thedispersions made with example PR57:1 pigments were retained in thecoatings, after evaporation of n-butyl acetate by oven drying, asinferred by the NLSI data.

It will be appreciated that various of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be desirablycombined into many other different systems or applications. Also thatvarious presently unforeseen or unanticipated alternatives,modifications, variations or improvements therein may be subsequentlymade by those skilled in the art which are also intended to beencompassed by the following claims.

1. A nanoscale pigment particle composition, comprising: an organicmonoazo laked pigment having at least one functional moiety, and asterically bulky stabilizer compound having at least one functionalgroup, wherein the functional moiety on the pigment associatesnon-covalently with the functional group of the stabilizer; and thenanoscale pigment particles have an average particle size of from about10 nm to about 500 nm and have coloristic properties that are changeablein accordance with both particle composition and average particle size.2. The composition of claim 1, wherein the nanoscale pigment particleshave an average particle diameter, as derived from transmission electronmicroscopy imaging, of less than about 200 nm.
 3. The composition ofclaim 1, wherein the nanoscale pigment particles have an averageparticle size (d₅₀ or Z-average), as derived by dynamic light scatteringanalysis methods, of less than about 250 nm.
 4. The composition of claim1, wherein the nanoscale pigment particles have an average particlesize, as derived by transmission electron microscopy imaging, of fromabout 25 nm to about 150 nm.
 5. The composition of claim 1, wherein thenanoscale pigment particles have a geometric standard deviation, asderived by dynamic light scattering analysis methods, of from about 1.1to about 1.8.
 6. The composition of claim 1, wherein the nanoscalepigment particles have a shape selected from the group consisting ofrods, platelets, needles, prisms, ellipsoids, and nearly spherical, andhave an aspect ratio (length:width) of from about 1:1 to about 5:1. 7.The composition of claim 1, wherein the coloristic properties aremeasured when the nanoscale pigment particles are dispersed in a polymerbinder.
 8. The composition of claim 1, wherein the coloristic propertiesare directly correlated with variable average particle size, as derivedby dynamic light scattering analysis methods.
 9. The composition ofclaim 1, wherein the coloristic properties are selected from the groupconsisting of L*, a*, b*, chroma C*, hue angle, normalized Light ScatterIndex (NLSI), and combinations thereof.
 10. The composition of claim 1,wherein the nanoscale pigment particles exhibit a hue angle, as derivedfrom a 2-dimensional b* a* color gamut space, ranging from about 345° toabout 0°.
 11. The composition of claim 1, wherein the nanoscale pigmentparticles exhibit a hue angle measured on a 2-dimensional b* a* colorgamut space of from about 345° to about 355°.
 12. The composition ofclaim 1, wherein the nanoscale pigment particles exhibit a NLSI value,determined as a degree of spectral absorbance due to particle lightscattering in a near-infrared spectral region between 700-900 nm,ranging from about 0.1 to about 3.0.
 13. The composition of claim 1,wherein the nanoscale pigment particles exhibit a NLSI value of fromabout 0.1 to about 1.5.
 14. The composition of claim 1, wherein thenanoscale pigment particles have enhanced chroma as compared to asimilar organic monoazo laked pigment not having the sterically bulkystabilizer compound and not having nanoscale-sized particles.
 15. Thecomposition of claim 1, wherein the nanoscale pigment particles exhibita hue angle, as derived from a 2-dimensional b* a* color gamut space,ranging from about 345° to about 0° and a NLSI value, calculated fromspectral absorbance in the near-infrared spectral region between 700-900nm, ranging of from about 0.1 to about 3.0.
 16. The composition of claim1, wherein the nanoscale pigment particles exhibit a hue angle, asderived from a 2-dimensional b* a* color gamut space, ranging from about345° to about 355°, and a NLSI value, calculated from spectralabsorbance in the near-infrared spectral region between 700-900 nm,ranging from about 0.1 to about 1.0.